1. Field
This invention relates to communication systems, and more particularly to a method and apparatus for flexibly filtering scheduling messages in communication systems.
2. Description of Related Art
Some communication systems, such as broadband communication systems as an example, facilitate high-speed connectivity and data transport from a point-to-multipoint basis.
Exemplary broadband communication systems include, without limitation, cable modem systems that facilitate the transport of data between cable modems and information providers such as cable television networks and Internet web sites. FIG. 1 depicts a simplified block diagram of an exemplary cable modem system. The exemplary cable modem system 10 of FIG. 1 comprises a wide area network (WAN) 12, a cable modem termination system (CMTS) 14, a plurality of cable modems (CM) 16 and a plurality of customer premises equipment (CPE) 18 (such as, for example, personal computers and televisions). The WAN 12 connects the cable modem system 10 to other networks such as a cable television network 22 or the well-known Internet via an Internet backbone 20. The CMTS 14 connects the plurality of cable modems 16 to the WAN 12. Cable modems typically provide high-speed Internet and cable television connectivity to businesses and homes.
Exemplary cable modem systems are described in more detail in a specification produced by the Cable Television Laboratories, Inc., entitled “Data-Over-Cable Service Interfaces Specification—Radio Frequency Interface Specification SP-RFIv11-105-000714,” published in the year 2000, and referred to below as the “DOCSIS specification”, hereby incorporated for reference herein in its entirety for its teachings on cable modem systems. As described in the DOCSIS specification, data packets transport data between cable modems and their associated CMTS. In accordance with the DOCSIS specification, upstream transmissions occur when data is transmitted from customer premises equipment. Downstream transmission is defined as the transmission of data to the customer premises equipment (e.g. from a cable television network). In cable modem systems, well-known protocols such as TDD and TDMA aid in scheduling data packet traffic on the upstream and downstream transmission paths.
Due to the wide variety of CPE service requirements, and due to the large number of CPEs serviced by any one CMTS, the bandwidth scheduling process in a communication system such as that shown in FIG. 1 can become overly burdensome and complex. This is especially true with regard to the scheduling of upstream bandwidth. A CMTS schedules upstream bandwidth by assigning transmit opportunities (i.e., time intervals) on the upstream transmission path to its associated cable modems. The CMTS transmits an upstream scheduling message comprising information regarding assigned transmit opportunities to its associated cable modems on the downstream. The cable modems use this information to determine their assigned transmit opportunities. An example of an upstream scheduling message is the well-known “Upstream Bandwidth Allocation Map” (MAP) message. The MAP message comprises a plurality of information elements (“IE”) that describe information regarding the transmit opportunities of cable modems that are associated with the CMTS transmitting the message. Methods of filtering upstream scheduling messages help provide high-speed connectivity and data transport in communication systems.
In accordance with one known method of filtering upstream scheduling messages, a CMTS periodically transmits a MAP message to all of its associated CMs on the downstream transmission path. An associated cable modem decodes and filters the MAP message. The method subsequently stores information regarding IEs associated with the CM. Each CM performs the above-described decoding and filtering to determine its transmit opportunities. In accordance with this method, IEs comprise information such as service identifiers, well-known addresses, interval usage codes, transmission times and transmission durations. This information is used by the modems to identify assigned transmit opportunities.
As is well known, a service identifier (SID) represents an address that identifies a cable modem or set of cable modems. SIDs typically comprise three types of addresses: “unicast” “multicast” and “broadcast”. Unicast addresses are defined herein as addresses that uniquely identify a cable modem. A unicast address aids a cable modem in determining time intervals that are dedicated solely for the cable modem associated with the unicast address. Multicast and broadcast addresses are well-known addresses. Broadcast addresses are defined herein as addresses that identify all cable modems that are associated with the CMTS. Multicast addresses are defined herein as addresses that identify a group of cable modems that are associated with the CMTS. A well-known address aids a cable modem in determining time intervals during which all or a group of cable modems are allowed to transmit on the upstream transmission path (e.g., contention time intervals). An Interval Usage Code (IUC) specifies an upstream burst parameter (e.g., QPSK and QAM-16) for the transmit opportunity. In accordance with the above-described method of filtering upstream scheduling messages, cable modems filter for IEs typically utilizing hardware means.
Disadvantageously, the above-described existing method for filtering upstream scheduling messages is relatively inflexible because the filtering is processed in hardware. New hardware design must be developed for different communication systems or when upgrades to the system occur. This inflexibility increases costs associated with the production of cable modems because different hardware must be designed and installed in cable modems produced for new markets, varying communication systems and upgraded systems.
Therefore, a need exists for a method and apparatus for flexibly filtering upstream scheduling messages in a communication system that can be easily implemented, relatively fast and overcomes the disadvantages of other methods and apparatuses such as the above-described method. The present disclosure provides such an upstream scheduling message filtering method and apparatus.